A forum for owners of Yamaha TTR250 trail and enduro bikes!

j180 · Senior Member

Maybe a stoopid question I heard

Terrence R · Senior Member

Your ttr should have the speedo set up for front wheel spinning speed. Meaning that gearing won't affect its accuracy.

TTRfan · Super Guru

Hi John

If you still have the 1993 OE then the digital speedo is driven off the front sprocket so that any changes to the gearing will affect the speedo readings. If this is a worry then you can get your speedo nearly 100% accurate using a Speedo DRD.

Blue TTRs have their speedo cable driven off the front wheel so only a change of tyre size from standard might have an effect on speedo readings.

Brian

j180 · Senior Member

Thanks Brian, if I keep the 14t front and go up at the back will this keep the Speedo true as its driven from the gearbox.

alanwebbo · Veteran Member

The digital speedo counts the revolutions of the gearbox sprocket shaft. yamaha calibrated the speedo by knowing how far the bike goes for every revolution of the shaft. This is a function of the sprocket sizes and rolling radius of the rear wheel. If you change either of the sprockets or the rolling radius of the wheel the speedo will be out. The speedo drd allows you to programme a correction factor into the signal from the pick up to compensate for the changes you make gearing. A cheaper but much cruder solution would be to use a bicycle speedo available for less than a tenner. once you have calibrated the bicycle speedo you could cross refence back to digital speedo.. Ie. you really only need to know what the digital speedo reads when the bicyle speedo reads 30' 40' 50. Mph. Etc

j180 · Senior Member

Thanks mucker, will need to work out what to do later.